Because we are not autotrophic organisms, i.e., can do photosynthesis which transforms inorganic substances in organic by the energy of the light ( vegetables and algae ) Neither the chemosynthesis which transforms them by the energy released in 40 oxidation; fungi and some bacteria ). We are heterotrophic and need the autotrophs to make us food ( carbohydrates, fats and proteins ). Also we can absorb mineral salts and trace elements dissolved in water through the digestive system.
Because we are not autotrophic organisms, i.e., can do photosynthesis which transforms inorganic substances in organic by the energy of the light ( vegetables and algae ) Neither the chemosynthesis which transforms them by the energy released in 40 oxidation; fungi and some bacteria ). We are heterotrophic and need the autotrophs to make us food ( carbohydrates, fats and proteins ). Also we can absorb mineral salts and trace elements dissolved in water through the digestive system.